Summary Impact Type

Research Subject Area(s)

Download original

Summary of the impact

Research at GCU led to a novel method for backfilling pipeline tunnels
providing the ability to fill tunnels three times more quickly than the
traditional method resulting in a cost saving of £1.5M on a single
project. This approach is now best practice at Murphy Pipelines Ltd (MPL)
and features in current tenders to a value of £30M. The change in fill
material lowered the carbon footprint by 5000 tonnes in a CEEQUAL award
winning project, in addition, the removable fill material allows the
recycling and re-use of tunnels, adding to the assets of the company and
reducing costs.

Underpinning research

Research on pneumatic conveying by experiment and simulation has been
on-going since the foundation of the Centre for Industrial Bulk Solids
Handling at GCU in 1990 and is currently led by Professor Don McGlinchey.
Pneumatic conveying as a means to transport particulate materials is
conceptually very simple; gas, usually air, is set in motion with
sufficient energy to entrain the particles and carry them along in the
flow stream. The industrial use of this technology is long established and
applied across a range of sectors; power generation, plastics, bulk
chemicals, and pharmaceuticals but still relies significantly on empirical
and heuristic approaches to improve the efficiency of pneumatic conveying
systems. The principle task when designing or optimising pneumatic
conveying systems is the determination of the system operating point in
terms of gas mass flow rate and overall line pressure drop to achieve a
desired throughput of particulate solids. Many correlations exist in the
literature to predict system operation; however, they are individually
limited in application. The research programme undertaken at GCU beginning
in the 1990s and continuing to date, resulted from the desire improve the
design method. The early research leaders were Dr David Mason, Prof Avi
Levy and the late Prof Predrag Marjanovic who developed a general
framework for simulation and modelling gas-solids flow. [1-3]. This work
developed a one dimensional computational Eulerian two — phase flow of
interdisperse continuum for general flow in straight pipelines, with other
pipeline features such as bends requiring to be modelled empirically.
McGlinchey and co-workers have refined the simulation methods and improved
the investigation of the detail of flow features, [4-5], by using either
granular kinetic theory or the discrete element method to model the solids
in combination with traditional computational fluid dynamics to create
three dimensional models of pipelines and features. Pneumatic conveying
systems can be modelled by a combination of the techniques noted above.
The research and applied knowledge base at GCU were recognised by MPL as a
vital factor in developing a novel tunnel backfill system. To complete the
final system design for Murphy Pipeline Ltd, GCU carried out both
simulations and experimental characterisation based on methods developed
at GCU using an industrial scale pneumatic conveying research facility.
This facility has been used for numerous research projects including the
conveying of sand and sand like material, and was suitable for scaling to
the duty required by MPL. Output of GCU research is based on a
computational fluid dynamics approach to simulating pneumatic conveying of
dry particulate solids with experimental validation and was shown to have
good agreement in the dilute phase region of operation proposed for the
system design for MPL.

Details of the impact

The Harefield to Southall Gas Pipeline in London was a major civil
engineering project undertaken by murphy Pipeline Ltd involving the design
and construction of 18km x 1220mm diameter gas pipeline and connection
into the existing network. The pipeline was laid in tunnels under major
arterial roads, railways (including London Underground), water courses and
the Grand Union Canal

In summary, the benefits for MPL of using the technology developed from
GCU research were:

Provide competitive contract tenders to a value of £30M for projects
worldwide.

The backfill technique developed using the research and design at GCU was
first used in tunnels in a project to meet rising gas demand in West
London, where Murphy Pipelines Ltd was contracted by National Grid to
construct an underground, high-pressure, steel pipeline between Harefield
and Southall. As well as providing the additional peak capacity necessary
to meet licence conditions, the pipeline strengthens security of supply
for customers in West London by ending their reliance on a single source
of high-pressure gas supply.

In order to meet engineering and safety requirements Murphy Pipelines Ltd
(MPL) had to find a way to provide mechanical support for a gas pipeline
running along underground tunnels from Harefield to Southall comprising:
18.2 km of 1220mm diameter gas pipeline, 3 segmental tunnels approx
2.225km and 8 pipejacks approx 0.935km

Conventional methods for support and backfilling were impractical and
time consuming, therefore pneumatically conveying a dry particulate
material was considered.

The research and expertise in pneumatic conveying residing in Glasgow
Caledonian University, as highlighted on the website www.particulatesolidshandling.com,
led MPL to commission GCU to undertake an initial feasibility study
starting in May 2006 involving simulation of a proposed conveying system,
followed by pneumatic conveying and wear assessment trials in our solids
handling and pneumatic conveying test labs, finishing in September 2007.
GCU provided unique conveying characteristics for a range of conveying
configurations and distances allowing the most appropriate particulate
material and conveying technology to be selected.

Initially, estimates of pipe bore and gas flow rates were made for
required conveying distances by scaling published data for a similar
material and by use of a computer model developed at GCU which
demonstrated the potential of the method to meet the required duty.

A pneumatic conveying system at GCU was successfully used to test the
performance of potential backfill materials through different pipeline
configurations.

An established scaling procedure was carried out on the data from
experimentally determined conveying characteristics for a change in
pipeline length and a change in pipe bore. Conveying characteristics were
generated for seven different design configurations of varying length and
pipe bore. A particular design configuration was highlighted in
discussions with Murphy Pipelines as being the most likely or favoured
design.

The application of GCU's research was challenging due to the complexity
of the design and operation of systems; for example, very regular changes
in pipeline lengths as the tunnel is filled will result in dramatic
changes to the optimal operating point and the likelihood of pipeline
blockages and failure of operations is significant if the system is not
correctly designed and operated.

Based on the GCU design parameters and recommendations, MPL commissioned
the manufacture of a tunnel backfill system from Aptech Ltd, a specialist
in the design, supply and installation of particulate solids handling
equipment based in Leicestershire.

The traditional method used for tunnel filling by cement grouting but
this comes at a high price environmentally and financially. Following the
work at GCU dry sand was used to fill the large diameter tunnels on the
project. As well as being cheaper to buy and work with, the embodied
carbon associated with its production is 60 times less than that of grout.
A recycled glass product called EcoSand was also used as an innovative and
more sustainable alternative to sand. The carbon saving was equivalent to
that of sand, but with the added benefit of making use of a waste product
instead of a non-renewable resource. Being quicker to install, this
technology represented a 10-week saving on the project programme, as well
as saving 5,000 tonnes of embodied carbon. This, in part, made the
Harefield to Southall Gas Pipeline Project a Winner of a CEEQUAL
Outstanding Achievement Award 2011 for Waste Management. The gas pipeline
became operational in December 2009.